Question

The power of a lens is ______.

विकल्प

• directly proportional to its focal length in centimetres

• inversely proportional to its focal length in centimetres

• inversely proportional to its focal length in metres

• directly proportional to its focal length in metres.

Answer 1

The power of a lens is inversely proportional to its focal length in metres.

Explanation:

The power of a lens is the reciprocal of its focal length in metres:

$$\text{P} = \dfrac{1}{f}$$

So power increases when focal length decreases.